Air conditioning system



May 7, R MlLLER AIR CONDITIONING SYSTEM I 7 Filed Oct. 15, 1936 2 Sheets-Sheet 1 CONDENSER y 1940. w. R. MILLER v 2,200,118

KIR CONDITIONING SYSTEM Filed Oct. 15, 1935 2 Sheets-Sheet 2 CON DENSER W052 and Mz'ZZer Patented May 7, 1940 AIR CONDITIONING SYSTEM Wayland R. Miller, Nashotah, Wis., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn, a corporation of Delaware Application October 15, 1936, Serial No. 105,840

12 Claims.

This invention relates to the art of air conditioning and is more particularly concerned with the cooling and dehumidification of air. In order to reduce excessive temperature or humidity, removal ofheat from the air is necessary. Removal of excessive humidity, however, requires a. different type of cooling action than does the removal of excessive temperature. In order toreduce temperature it is necessary only to remove heat from the air and part of the super-heat of the water vapor contained therein. For reductionin humidity, however, it is necessary to condense a part of the water vapor contained in the air. This requires first that the 15 temperature of the air be reduced to the dewpoint. Upon abstraction of heat from the air after the dew-point temperature has been reached, condensation of the water vapor will take place. I

When air is passed through a cooling coil or some other type of cooling device, both temperature and humidity may be reduced; The cooling device first acts to remove only sensible heat until the dew-point temperature has been reached, and then acts to remove the latent heat of evaporation of the water vapor in the air, therebycausing condensation of such water vaporf consequently resulting in dehumidification. Assuming that the heat removal capacity of the cooling device remains fairly constant and that the dew-point temperature of the air is likewise fairly constant, 'the amount of dehumidification caused by such cooling device will depend upon the temperature of the entering air.

- For instance, if the temperature of the entering air is at the dew-point, substantially all of the heat removal capacity of the cooling device will go towards removal of watervapor. If, however, the temperature of. the entering air is substantially above. the dew-point, the coil must first act to remove sensible heat until the dewpoint temperature has been reached before condensation of water vapor will begin. The amount of condensation will therefore be reduced. It

follows that by varying the temperature of the air entering the cooling device, the dehumidifying action of such device may be controlled.

In'accordance with my invention, I effect precooling, cooling and reheating by a single refrigeration system. In this form an auxiliary evapo- 'rator is placed in the conditioning chamber in advance of the main cooling coil, while. a condenser is placed on the down-stream side of such main cooling -coil.' A liquid refrigerant is I passed through an expansion valve first into the auxiliary evaporator wherein part of it is evaporated, causingpre-cooling of the air. The mixture of liquid and gaseous refrigerant is then passed into the reheater wherein the vaporized refrigerant is condensed. The liquid refrigerant from this reheater is then passed into the main cooling coil wherein it is evaporated,

thereby causing cooling of the air.

It is therefore an object of my invention to provide a single refrigeration system for an air conditioning apparatus which acts to pre-cool, cool and reheat the air.

A further object of my invention is to provide a control means for such a system for controlling the pre-cooling and reheating to main- 15 tain a desired condition of the air.

Another object of my invention is the provision of .a novel multiple type refrigeration system and control system for controlling the action thereof.

Another object is the provision of an air conditioning system utilizing a primary and secondary cooling system wherein the secondary system includes an evaporator and a condenser located relatively to each other in a manner for providing a positive circulation of refrigerant between the condenser and evaporator. Other objects will appear from the following detailed description and the appended claims. For a complete disclosureof my invention, referv ence is made to the following description and to the accompanying drawings, in which:

Figure 1 indicates diagrammatically an air conditioning system utilizing primary and secondary cooling systems wherein the secondary system operates by thermosiphonic action; and

Figure 2 is a diagrammatic showing of. an air conditioning system wherein the primary and secondary cooling systems are integral parts of a single refrigeration system.

Referring to Figure 1, reference character I indicates generally an air conditioning chamber. Conditioning chamber l is L-shaped and houses a main cooling coil 2, a pre-cooler 3, and a reheater 4, reheater I being located above the 4 pre-cooler 3. The upper end of conditioningchamber l is reduced as at I and connects with an elbow 8 leading to a fan I. A discharge duct 8 from fan 1 leads to a register 8 in the air conditioned space Ill. The return air register ll is disposed in the space l0 and is connected to a return duct II which joins a fresh air duct I3 and an inlet duct M which leads to the inlet of the conditioning chamber I. Suitable dampers I5 and It may be provided in the return and fresh air ducts respectively to control the proportions of the return and fresh air admitted to the conditioning chamber in accordance with usual practice.

The pre-cooler 3 is illustrated as formed of inlet and outlet headers 20 and 2| connected by a series of fin tubes 22. The condenser 4 is formed in a similar manner. It is to be understood, however, that the form shown is merely illustrative and that these devices may take any other desired form. The main cooling coil 2 is illustrated as comprising inlet and outlet headers 24 and 25 connected together by a series of sinuous tubes 26 having thereon a series of fins 21. This again is merely an illustrative form, and my invention is not limited thereto.

For supplying liquid refrigerant to the main cooling-coil 2 and for withdrawing the evaporated refrigerant therefrom, I have shown the usual form of compression refrigeration system. This system comprises a compressor 38 driven by an electric motor 3| through a belt drive 32. A discharge pipe 33 leads from the discharge side of the compressor to a condenser 34 which may be of any known form. To the outlet of the condenser 34 is secured a supply pipe 35 for conducting the liquid refrigerant to the main cooling coil 2. Interposed in the pipe 35 is an expansion valve 36 which is in this case shown as a thermostatic expansion valve of known form. A suction line 31 is connected to the discharge header 25 of the main cooling coil 2 and leads to the suction side of the compressor 38.

The operation of this form of-refrigeration system is well understood. The compressor 30 acts to remove vaporized refrigerant from the cooling coil and to increase the pressure of such refrigerant. This compressed refrigerant then passes into the condenser where heat is removed therefrom, causing liquification of the compressed refrigerant. This liquified refrigerant is then passed through the expansion valve wherein its pressure is reduced. Upon entry of this liquid refrigerant into the main cooling coil it absorbs heat and changes its state from a liquid to a vapor, this action causing lowering in temperature of the cooling coil. This .vaporized refrigerant is then drawn into the suction side of the compressor and the cycle is repeated. The thermostatic expansion valve 36 is indicated as having its thermostatic bulb 38 located at the outletof the evaporating coil, This'arrangei'nent acts to admit suflicient refrigerant into the cooling coil to keep such coil substantially full of liquid refrigerant. V

The operation of thecompressor motor 3| is indicated as being controlled by means of a room thermostat 40 located in the air conditioned space It]. The thermostat 40 may take any known form and is inthis case illustrated as comprising a bimetallic element 4| having one end fixed at'42 and its other end connected to a contact blade 43. The contact blade 43 carries a contact 44 cooperating with a stationary contact 45. Upon an increase in temperature bimetallic element 4| will act to swing the contact blade 43 to bring the contact 44 into engagement with the contact 45. Upon a decrease in temperature from that at which the thermostat is set, the bimetallicelement 4| will cause the contact 44 to become disengaged from contact 45. The bimetallic element 4| is connected by a wire 46 to the secondary 41 of a step-down transformer 48. The stationary contact is connected by a wire 49 to one end of the coil 50 of a relay 5|, the other end of said relay coil being connected by a wire 52 to the other side of the transformer secondary 41.

Relay 5| includes an armature or plunger 53 located in the magnetic field of the coil 58. Armature 53 is connected to a'link 54 which has its other end pivotally connected to a switch arm 55. Switch arm 55 is pivoted at one end at 56 and at its other end cooperates with a contact 51. The contact 51 is connected by a wire 58 to a line wire 59. The switch arm 55 is connected to one terminal of motor 3| by means of a wire 60. The other terminal of motor 3| is connected by a wire 6| to the line wire 62. Line wires 59 and 6.2 are illustrated also as energizing the primary 63 of the step-down transformer 48.

When the temperature in the conditioned space In is above a predetermined value the movable contact ;44 of the thermostat 40 will engage the contact 43. This will close an energizing circuit for the relay coil 5|) as follows: transformer secondary 41, wire 46, bimetallic element 4|, contact 44, contact 45, wire 49, relay coil 58 and wire 52 back to transformer secondary 41. Energization of the relay coil 50 will cause the armature 53 to move to the right, thereby bringing the switch arm 55 intoengagement with the contact 51. This will close the operating circuit for the compressor motor and place the compressor into operation.

If the temperature in the space l0 falls below the value for which the thermostat 40 is set, the bimetallic element 4| will cause disengagement of contact 44 from the contact 45. This will break the energizing circuit for the relay coil 50, this permitting the-armature 53 to be moved towards the left under the action of a spring (not shown) resulting 'in the switch arm 55 disengaging the contact 51. This will break the compressor motor operating the circuit and place the compressor out of operation. 3

From the foregoing it should be apparent that the cooling coil 2 will be placed in operation so long 'as'the temperature in the space I0 is above a predetermined value and that when the temperature in suchspace becomes sufliciently low the cooling coil 2 will be placed out of operation.

The upper or outlet header 2| of the pre-cooler 3 is connected by means of a pipe 65 to the inlet header 'of the reheater 4. A pipe 66 is connected to the outlet header of the reheater 4, this pipe leading to the inlet header 20 of the pre-cooler 3. A solenoid valve 61 is interposed in the pipe 65 while a similar valve 68 is interposed in the pipe 66. It will thus be apparent that the precooler and reheater are connected together to form a closed system which is entirely separate from the system for actuating the main cooling coil 2. This system'may be charged with any suitable secondary refrigerant, such for instance as Freon, menthol chloride, ammonia, etc.

The solenoid valves 61 and 68 may be of any known form and are herein shown as comprising a type which opens when energized and which closes when deenergized. These valves are con trolled by means of a humidostat generally indicated at 10, this'humidostat being located in the conditioned space I. Humidostat 10 is formed of a mercury switch supporting arm 1| which is pivoted at oneend at 12 and which carries a mercury switch 13 of known form. The

other end of the arm 1| is connected to one end of a spring 14. Spring 14 at its other end is secured to a suitable fixed support 15. Also ing position.

18 or other moisture responsive elements, these elements being secured at their ends to suitable clamping members 11 and 18, the clamping member 11 being connected to the free end of arm ll while the clamping member 18 is secured to a suitable stationary member 19. Upon an increase in humidity, the moisture responsive elements 16 will expand, thereby permitting the spring 14 to raise the free end of the arm 'H thus tilting the mercury switch to circuit clos- Conversely, a decrease in humidity will cause the moisture responsive elements 16 to contract, this action causing tilting of the arm II and the mercury switch I3 to circuit opening position. The mercury switch 13 is connected to control the solenoid valves 61 and 68.

One electrode'of mercury switch 13 is connected by a wire to one end of the transformer secondary 41. The other end of the transformer secondary 4'lis connected by wires 8| and 82 to one terminal each of the solenoid valves 61 and 68. The remaining terminals of valves 61 and 68 are connected together by wires 83 and 84, wire 84 also acting to connect these terminals to the other electrode of the mercury switch 13.

It should be apparent, therefore, that upon an increase in humidity the mercury switch 13 will be tilted to circuit closing position, this action causing opening of solenoid valves 61 and 68.

Conversely, when the humidity decreases below a predetermined value mercury switch 13 will be tilted to circuit opening position, thereby causing the valves 61 and 68 to close.

While I have shown the secondary system as being controlled by solenoid valves 61 and 68, it is to be understood, that other types of valves may be used, and that if desired, only one valve may be employed.

Operation Whenever the space temperature is above a predetermined minimum value, such for instance as 75 F., the room thermostat 40 will cause operation of the compressor motor and hence chilling of the cooling coil 2. Due to the operation of the fan 1, air will be drawn through the return register and duct l2 into the conditioning chamber, across the cooling coil 2, wherein its temperature will be reduced. The cooled air will then be discharged through the discharge duct 8 and register 9 back into the conditioned space Ill. The air in passing through the cooling coil 2 will be first reduced in temperature until the dew-point is reached. After'this point is reached the air will further be reduced in temperature and the latent heat of evaporation of the water vapor contained in such air'will be chilled.

Should the humidity within the space H! be above a predetermined value, the mercury switch 13 will be tilted to circuit closing position as illustrated. This will cause the solenoidvalves 61 and 68 to be energized, thereby assuming an open position. With valves 61 and 88 open the pre-cooler 3 and the reheater 4 are placed in communication with each other. As the precooler 3 is in the path of the air passing to the cooling coil 2 it is exposed to air of relatively high temperature. The reheater 4, on the other hand, is located in the path of the air which has been .cooled by the main cooling coil 2 and is therefore exposed to air of substantially lower temperature than that contacting the pre-cooler 3. Due to the. relatively high temperature to which the pre-cooler 3 is subjected, the liquid refrigeranttherein will be evaporated and absorb heat from the air. The vapor will then pass .through the pipe 85, through solenoid valve 81 into the reheater 4. As the reheater 4 is subjected to air of lower temperature than caused evaporation of the refrigerant, heat will be removed from the vaporized refrigerant, thereby causing it to condense and thus give up to the cooled air the same amount of heat that it absorbed from the incoming air. This liquid refrigerant wilLthen flow through the pipe 86 back to the pre-cooler 3, where it will be re-evaporated and this cycle will be repeated continuously. It will be observed that the reheater 4 is located on a level above that of the pre-cooler 3. As the pipe 65 will'contain the evaporated refrigerant while the pipe 66 will contain refrigerant in a liquid state, a thermo-syphonic circulation of refrigerant through the secondary refrigerating system formed of pre-cooler 3 and reheater 4 will take place. It should be apparent, therefore, that the secondary refrigeration system will act to remove heat from the air passing to the main cooling coil 2 and will act to give up the heat which has been removed to the air after it has been cooled by the cooling coil 2, this action ocgurring without the application of any external orce.

The effect of the operation of the secondary refrigerating system is to reduce the temperature of the air passing to the main cooling coil and to reheat the air after it has been cooled by said main cooling coil. This action causes the cooling coil 2 to expend its efiorts towardsdehumidification of the air to a greater extent than would occur without operation of the secondary refrigerating system. In other words, the action I of the secondary system is to remove sensible heat from the air before its contacts with the cooling coil 2, thereby decreasing the amount of sensible heat which must be removed by the coil 2 before dehumidification starts. In this manner operation of the secondary system increases the dehumidifying effect of the cooling coil 2. Inasmuch as all the heat which is absorbed by the pre-cooler 3 is delivered back to the air by the reheater 4, the operation of the'secondary system has substantially no effect upon the total quantity of heat removed from the air. Such system merely increases the dehumidifying action of coil 2.

As a specific example of the effect of operation of the secondary system, it may be assumed that the incoming air is at 90 F. and 70% relative humidity. Assuming that the pre-coo-ler is designed to remove 10 of sensible heat from the air for the given air flow, the air after passing through the pre-cooler will be 80 F. and 94%,

relative humidity. In passing through the cooling coil 2 suflicient heat mai be removed from the air to reduce its condition from 80?, F.--94% relative humidity, 130 grains of moisture per pound, to 55 F.-% relative humidity, 65'

grains of moisture per pound. In passing through the reheater 4 the same amount of heat will be returned to the air as was absorbed from it in the pro-cooling coil 3. Hence the final temperature of the air leaving the conditioning chamber will be approximately 65 F.--75% relative humidity, 65 grains of moisture per pound.

If the secondary refrigeration system is placed out of operation, as by closing valves 61 and 68, no heat will be absorbed by the pre-cooler and no heat will be given up to the air by the reheater Q. Assuming the same initial conditions of the entering air, that is 90 F.-'70% relative humidity, and the same cooling effect of cooling coil 2, the air leaving such cooling coil will be reduced to 58 F.l% relative humidity, '74 grains of moisture per pound. Summarizing for the condition stated, when the secondary system is in operation the final air condition will be 65 F.-75% relative humidity, 65 grains of moisture per pound, while with the secondary system out of operation, the final air condition will be 58 F.100% relative humidity, 74 grains of moisture per pound. It should be apparent, therefore, that the effect of the secondary system is to increase the amount of dehumidification and to decrease the amount of reduction in sensible heat by the cooling coil 2.

As long as the temperature within the space I0 is above a predetermined minimum value and the humidity is above a desired value, operation of both the main cooling coil 2 and the secondary refrigeration system will continue. Due to the increased dehumidifying effect of coil 2 caused by the operation of the secondary system, the excessive humidity conditions within the space I0 will eventually be overcome. At this point the humidostat I0 will act to cause closing of the solenoid valves 61 and 68. This will prevent circulation of refrigerant from the pre-cooler 3 to the reheater 4, thereby placing the secondary refrigeration system out of operation thereby decreasing the dehumidifying effect of the cooling coil 2 and increasing the portion of the cooling effect of said coil which goes towards reduction in sensible heat of the air. This operation will continue until the temperature in the space is lowered to the desired value, when the thermostat 40 will act to place the entire system out of operation.

From the foregoing it will be seen that the thermostat 40 assumes dominating control over the entire-system and prevents any cooling whatsoever after the space temperature is below a I desired value, and it will further be apparent that when the system is in operation due to the temperature within the space being above the predetermined minimum, the cooling effector the main cooling coil will be shifted from either temperature reduction or humidity reduction in accordance with the humidity within the conditioned space. In this manner-both the temperature and humidity may be maintained within the desired limits.

Figure 2 In Figure 2 I have shown a system which obtains the same results and which operates in a manner similar to that of Figure 1. With this system, however, no secondary refrigerating system is required, the pre-cooler and the reheater forming part of the main refrigerating system. In this figure corresponding parts are indicated by the same reference characters as in Figure 1, these reference characters, however, being primed. As in the case of Figure 1, the conditioning chamber I is provided with a main cooling coil 2', a pre-coo1er'3', and a reheater 4'. The conditioning chamber I is connected at one end to a fan I which discharges into a duct 8' leading to a register 9 in the conditioned space I0. A return air register II is connected to a return duct I2 which discharges into the inlet of the conditioning chamber I. The compressor motor 3| and the compressor 30 is controlled by means of a room thermostat 40, the control arrangement being identical with that illustrated in Figure 1. Hence no further description thereof is made at this point.

The compressor 30 is connected at its discharge side to a discharge line 33' leading to the condenser 34'. The outlet of the condenser 34' is connected by means of a pipe 35' to an expansion valve'36. The outlet of the expansion valve 36' is connected to a T connection I00. One branch of the T connection I00 leads to the inlet of the p re-cooler 3. The outlet of the precooler 3' is connected by a pipe IOI to the inlet of the reheater 4. The lower or outlet header of the preheater 4' is connected to a pipe I02 having interposed therein a flow restricting orifice plate I03. Pipe I02 is connected to a T connection I04, one branch of which is connected by the pipe I05 with the inlet of the main evaporating coil 2'. A pipe I06 connects the other branches of the T connections I00 and I04 together. This pipe has interposed therein a solenoid or other electrically actuated valve 61'. The outlet of the main cooling coil 2' is connected by the suction line 31' to the suction side of the compressor 30'.

The solenoid valve 61 is preferably designed so as to open when energized and to close when deenergized. This valve is controlled by means of the humidostat III which, is located in the conditioned space I0. formed similarly to the humidostat I0 of Figure 1 except for the fact that the position of the mercury switch I3 is reversed. That is, when the This humidostat is.

humidity is excessive, the mercury switch will In other from the condenser will pass throughthe expansion valve into the pre-cooler 3'. As its pressure has been reduced by the expansion valve, evaporation thereof will take place, thereby causing the pre-cooler 3' to absorb heat from the air entering the conditioning chamber I'. Due to the relatively small size of the pre-cooler 3' only partial evaporation will takeplace. Therefore a mixture of gaseous and liquid refrigerant leaves the evaporator 3' through the pipe IOI and passes into the reheater 4'. Due tothe eiTect of the cooling coil 2' the temperature of the air at the reheater 4' will be lower than the temperature at the pre-cooler 3, which caused partial evaporation of the refrigerant. This lower temperature will cause heat to be absorbed from the vaporized refrigerant, thereby causing condensation thereof and its return to the liquid state. The liquid refrigerant then passes from the evaporating coil 4' through the pipe I02 and the obtain satisfactory results.

restricting orifice I03 into the inlet of the evaporating coil 2'. As the outlet of the evaporating coil 2 is connected to the suction side of the compressor the pressure within the evaporating coil 2' will be considerably reduced, thereby causing evaporation of all the refrigerant within the cooling coil 2' and the passage of refrigerant in a vaporized state to the compressor. The purpose of the restricting orifice I03 is to restrict the flow of refrigerant from the reheater 4' into the evaporating coil 2', thereby preventing the flow of anything but liquid refrigerant from the reheater 4'. I

From the foregoing it should be apparent that when the humidity is excessive in the conditioned space Hi the solenoid valve 61' will be closed, thereby forcing the refrigerant through the precooler and reheater before entry into the main cooling coil 2, thereby causing operation of the pre-cooler 3' and the reheater 4. This will lower the temperature of the air entering cooling coil 2' and thus increase the dehumidification effect of the cooling coil 2'. I

When the humidity within the conditioned space l0 falls below the predetermined value, the mercury switch 13 will be tilted to cause opening of the solenoid valve 61'. With this valve opened the refrigerant will by-pass the pre-cooler and reheater and enter directly into the main cooling coil 2' due to the latter path having less resistance than the path through the pre-cooler, reheater, and orifice I03. The dehumidifying effect of the coil 2 will therefore be reduced.

It should thus be apparent that I have provided an air conditioning system in which both temperature and humidity are controlled and in which the humidity is controlled by varying the cooling effect of a cooling coil, this variation in cooling effect being obtained by controlling the amount of heat which is removed from the' air entering the cooling coil and which is returned to the air after passing through said coil. It will be further apparent that the differential in temperature caused by the cooling coil is employed for causing the flow of heat fromthe air on the inlet side thereof to the cooled air;

While I have shown the pro-coolerv and reheating system as being controlled by humidity and the main refrigerating system as controlled by temperature, it will be apparent that this arrangement may be varied considerably and still Also, while I have shown contro lers of the two-position variety, it is to be understood that other controllers such as a modulating type may be substituted therefor. Inasmuch as many other modifications will suggest themselves to those skilled in the art, I desire to be limited only by the scope of the appended claims and the prior art.

I claim as my" invention:

1. In an air conditioning system, in combination, a conditioning chamber through which air is adapted to be passed, a refrigeration system for varying the temperature and humidity of the air flowing through said conditionin chamber, said refrigeration system including a main evaporator, an auxiliary evaporator in advance of said main evaporator with respect to air flow, and a condenser downstream of said main evaporator, means for supplying refrigerant first to the auxiliary evaporator, means for conveying said refrigerant from the auxiliary evaporator to the condenser, and means fordischarging the refrigerant from the condenser into.

the main evaporator.

a 2. man air conditioning system, in combination, a conditioning chamber through which air is adapted to be passed, a refrigeration system for varying the temperature and humidity of the air flowing through said conditioning chamber, said refrigeration system including a main evaporator, an auxiliary evaporator in advance of said main evaporator with respect to air flow, and a condenser downstream of said main evaporator,

means for supplying refrigerant first to the auxiliary evaporat r, means for conveying said refrigerant from;tt e auxiliary evaporator to the condenser, mans for discharging the refrigerant from the condenser into the main evaporator, means for by-passing refrigerant around said auxiliary evaporator and condenser, and condimeans for supplying refrigerant first to the auxiliary evaporator, means. for conveying said refrigerant from the auxiliary evaporator to the condenser, means for discharging the refrigerant from the condenser into the main evaporator, bypass means for by-passin'g refrigerant around said auxiliary evaporator, temperature responsive means for controlling the supply of liquid refrigerant to said evaporators, and means influenced by humidity for controlling said by-pass means.

4. In an air conditioning system for a space, v

in combination, a conditioning chamber, means for causing air to flow through said conditioning chamber, a refrigeration system for cooling and dehumidifying the air flowing through said chamber, said refrigeration system including a first evaporator, a second evaporator, and a condenser located in said conditioning chamber, means for passing refrigerant from said first evaporator to said condenser, and means for passing refrigerant from said condenser to said second evaporator. 5. In an air conditioning system for a space, in combination, a conditioning chamber, means for causing air to flow through said conditioning chamber, a refrigeration system for cooling and dehumidif-ying the air flowing through said chamber, said refrigeration system including a first evaporator, a second evaporator, a condenser located in said conditioning chamber, said first evaporator being connected to said second evaporator and said condenser, control means for controlling the flow of refrigerant into one of said evaporators, and condition responsive means influenced by a condition in said space in control of said control means. I v V 6. In an air conditioning system, in combination, a conditioning chamber, means for causing air to flow through said conditioning chamber, a cooling coil in said chamber for cooling and dehumidifying the air flowing therethrough, means for supplying liquid refrigerant to said cooling coil, a reheater for reheating the air leaving said cooling coil, means for passing said liquid refrigerant through said reheater, means for bypassing the liquid refrigerant around said .re-, heater, valve means for, controlling the flow of refrigerant through said reheater and by-pass, and condition responsive means for controlling said valve means.

'7. In an air conditioning system, in combination, a cooling and dehumidifying device for cooling and dehumidifying a stream of air, a precooling device in advance of said cooling and dehumidifying device with respect to air flow, a reheater device downstream of said cooling and dehumidifying device for reheating the air, and means for passing cooling medium through said precooling device, said reheater device and said cooling and dehumidifying device in the order named.

8. In an air conditioning system for a space, in combination, a cooling and dehumidifying device for cooling and dehumidifying a stream of air, means for passing liquid cooling medium to said cooling and dehumidifying device, a reheater device downstream of said cooling and dehumidifying device for reheating the air, means for passing said liquid cooling medium through said reheater in series relationship with said cooling and dehumidifying device, a by-pass for said medium around said reheater, and means including condition responsive means for controlling the flow of medium through said by-pass.

9. In a refrigeration system, in combination, refrigerant condensing and back pressure reducing means, a first evaporator in heat exchange relationship with medium to be cooled, means for conveying liquid refrigerant from said condensing means to said first evaporator and including an expansion valve, a condenser, means for conveying refrigerant fromsaid first evaporator to said condenser, a second evaporator in heat exchange relationship with medium to be cooled, means for conveying refrigerant from said condenser to said second evaporator, and

means for connecting said second evaporator to said back pressure reducing means.

10. In a refrigeration system, in combination, refrigerant condensing and back pressure reducing means, a first evaporator in heat exchange relationship with medium to be cooled, means for conveying liquid refrigerant from said condensing means to said first evaporator, a condenser, means for conveying refrigerant from said first evaporator to said condenser, a second evaporator in heat exchange relationship with medium to be cooled, means for conveying refrigerant from said condenser to said second evaporator, and controllable means for passing refrigerant from said condensing means directly to said second evaporator.

11. In a refrigeration system, in combination, a first evaporator in heat exchange relationship with medium to be cooled, means including a first condenser for supplying refrigerant to said first evaporator, a second evaporator in heat exchange relationship with medium to be cooled, means for serially connecting said first and second evaporators in a manner to cause refrigerant to fiow from said first evaporator to said second evaporator, and condensing means interposed between said first and second evaporators.

12. In a refrigeration system, in combination, a first evaporator in heat exchange relationship with medium to be cooled, means for supplying refrigerant to said first evaporator, a second evaporator in heat exchange relationship with medium to be cooled, means for serially connecting said first and second evaporators, condensing means interposed between said first and second evaporators, and controllable means for passing refrigerant to said second evaporator without passing through said first evaporator and condensing means. WAYLAND R. MILLER. 

